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Cat 568A or B: Which is Right For HDMI?

The two cables may look alike, but they don't terminate the same. Here is what you need to know when using Category 568A and B.


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Someone asked if it was better to use Category 568A or 568B with HDMI. The short answer: neither. Any high-speed engineer learns early in his career that going direct and straight is the best. So why would manufacturers use a 568A or B wiring scheme?

You are the reason. They know that you are familiar with 568A or B and to use it for high-speed HDMI would require you to learn terminating RJ45s in sequential pairs, not 568.

So the bigger question is why are you trying to apply telephone and/or Ethernet applications to HDMI? My guess is that the wire looks the same, the connector looks the same, so why not terminate the same. That’s where the similarities end.

The connector that we typically use for Cat 5 ATD (balun) is an RJ45. This came from a family of connectors ranging from RJ11, RJ25, RJ61, etc. created to standardize telephone-related wires.

When introduced, the quality of the RJ connector was so impressive the FCC even incorporated it into its Part 68 rules. The RJ11 is a 6-pin device and can come in different arrangements for one, two or three analog telephone lines.

However, four analog voice lines used an 8-pin connector called the RJ61. The RJ45 term was essentially decided on by the EIA/TIA to be used for Ethernet, but it became the standard for both voice and data, and so came the 568 standard.

Here is where it gets interesting. Under 568A the two center pins 4 and 5 were isolated by splitting the orange pair to pin 3 and 6, trapping the blue pair on pin 4 and 5 and reversing its phase. The reason was to accommodate the voice telephone line should someone plug an RJ11 into a female RJ45 connector. Under 568B rules the only difference is the orange split pair is replaced by the green, and the orange is relocated where the green came from.





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Article Topics

News · Wire and Cable · HDMI · All topics

About the Author

Jeff Boccaccio, President, DPL Labs
Jeff Boccaccio, president of DPL Labs, can be reached at jeff@dpllabs.com.

9 Comments (displayed in order by date/time)

Posted by Chris  on  02/17  at  03:03 PM

So if 568A and 568B aren’t as reliable, why don’t manufacturers dictate that it must be done another way instead of putting out known to be inferior products in fear that we can’t RTFM!?!?!

Posted by Greg C  on  02/17  at  05:57 PM

Well, one well known manifacturer does not use 568 for their baluns. And they work every time.

Posted by Chris  on  02/18  at  05:45 PM

And who might that be?  We use Crestron and even they state 568B for their DM terminations.

Posted by Whitevan Lifestyle  on  02/18  at  07:53 PM

I’m with you Greg. Those are the only baluns I use.

Posted by Ernie Gilman  on  02/20  at  06:48 PM

This is a series of insults to every installer, after the HDMI folks invented a signal transmission method not meant to go more than about two meters.

Paragraph 2: it is the fault of the installer that we are using CAT5 at all.  It’s not that HDMI was invented without realizing that the cheapest installs almost always use short cables, the really fantasic installs hardly ever do, and HDMI inventors had zero clue about this. 

He also states that we could wire things up properly if we could just somehow stretch ourselves and learn how to hook up an RJ45 connector with wires in the order 1, 2, 3, 4, 5, 6, 7, 8.  But it’s too hard for us to learn that, he thinks.

And we should take advice from this guy?

Posted by Greg C  on  02/21  at  04:57 PM

Ernie, Jeff is a very bright engineer. He knows the limitations of HDMI better than most. If you ever get a chance to sit in one of his classes, do yourself a favor and do it! By the way, ask Brent about how many tech support calls he gets due to installers not following directions on pinout of his baluns.
And Crestron does use 568B for their DM, but it is a HDBaseT, not a balun.

Posted by Joe Fernand  on  02/28  at  02:01 AM

Installers RTFM – you have to be joking; most throw the manual out with the packaging then get on the phone and shout at Tech support and then throw the bits THEY can’t get working in a Jiffy bag and then wonder why they get charged a re-stocking fee!!!

We have units that use Jeff’s recommended wiring and get them thrown back at us by installers as useless as they don’t use ‘standard’ wiring and they have already pre terminated the whole job ‘the way they normally do it’ and ‘no were not willing to give it a go in future – our guys would forget to go with your daft wiring plan’.

Joe

Posted by JoJo The Dancing Bear  on  06/12  at  08:50 PM

So who is this manufacturer that that uses this wiring scheme?

What is the website to see and purchase them?

Posted by Ernie Gilman  on  06/13  at  11:43 PM

Joe Fernand, it’s a bit unfair of you (not to mention making you lose sales!) to imply that you make such products without telling us your company name.  Your name is not like Noel Lee (wait—did I get that right?)—we don’t know the company just by seeing the name.

JoJo, this whole article refers to various companies that make “baluns” for HDMI over CAT5, usually dual CAT5.

Greg C, I don’t doubt that Jeff is a very bright engineer.  The problem, for me, is that he seems to act like a True Believer when HDMI was just rammed down our throats with little regard to the reality that products don’t work together and there’s nothing about HDMI itself that even requires products to work together!  HDMI is a disaster except on paper and in technical classes.

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